One-piece fΘ-DEC scanning lens

Abstract

Both of the first surface and the second surface of the one-piece fΘ-DEC scanning lens of the present invention have to be in accordance with the following equation: ##EQU1## and the following criterion has to be satisfied: (1) 0.27≦fx/fy≦0.35 (2) | R 1 y | > | R 2 y | (3) 0.3<R 2 x/R 2 y<0.6, R 1 x/R 1 y≦0 Therefore, the one-piece fΘ-DEC scanning lens of the present invention is capable of replacing a convention two-element fΘ lens group so as to compensate the Wobble effect, scan linearly, and greatly decrease the setup volume of the scanner at the same time.

What is claimed is 
     
       1. A one-piece fΘ-DEC scanning lens which is adapted to be used to focus a light beam on an image surface, said light emitted by a light source and being reflected by a polygon mirror scanner to scan on a plane, wherein the scanning plane is defined as a plane scanned by said light beam while the secondary scanning plane is defined as a plane perpendicular to said scanning plane; furthermore, said one-piece fΘ-DEC scanning lens having a first surface and a second surface, while said first surface is near the light beam reflecting point of said polygon mirror scanner, and said first surface and said second surface are in accordance with the following equation: ##EQU4##  wherein, the origins of coordinates are defined as the apexes of said first surface and said second surface respectively, and the coordinates have X, Y, and Z axes which are perpendicular to each other, while said scanning plane is defined as YZ plane, and said secondary scanning plane is defined as XZ plane, wherein the concave surface of said first surface and said second surface are facing the light beam reflecting point of said polygon mirror scanner;   X, Y, and Z are coordinates of the X, Y, Z axes respectively;   Cx and Cy are the curvatures of the curved surfaces wherein the curve apexes are in XZ plane and YZ plane respectively;   Kx and Ky are the conic coefficients in XZ plane and YZ plane respectively;   An and An' are the 2n order rotational symmetry coefficients and 2n order non-rotational symmetry coefficients respectively; whereby following criteria are satisfied:     (1) 0.27≦fx/fy≦0.35   (2) | R 1  y | > | R 2  y |   (3) 0.3<R 2  x/R 2  y<0.6, R 1  x/R 1  y≦0 wherein,     fx represents the focal length in XZ plane;   fy represents the focal length in YZ plane;   R 1  y represents the radius of curvature of said first surface in YZ plane where the center of curvature on the same side as the incidence light beam is defined as a negative value;   R 2  y represents the radius of curvature of said second surface in YZ plane where the center of curvature on the same side as the incidence light beam is defined as a negative value;   R 1  x represents the radius of curvature of said first surface in XZ plane;   R 2  x represents the radius of curvature of said second surface in XZ plane.   
     
     
       2. The one-piece fΘ-DEC scanning lens as claimed in claim 1, wherein said one-piece fΘ-DEC scanning lens is manufactured from acrylic resin. 
     
     
       3. The one-piece fΘ-DEC scanning lens as claimed in claim 1, wherein said one-piece fΘ-DEC scanning lens is manufactured from molding glass.